1. Field of the Invention
The present invention relates to a forklift provided with a pallet lock device for locking a pallet lifted by a fork to prevent the pallet from being oscillated or accidentally being displaced while it is being conveyed.
2. Description of the Related Art
FIG. 15 is a side view schematically showing a conventional order picking truck 1. In the order picking truck 1, a fork 2 and an operator""s stand 3 are integrally elevated so that reloading of a load is conducted at a high position. Reference numeral 4 is a pedestal on which an operator gets in the operator""s stand 3. A pallet 6 into which the fork 2 is inserted is locked by a lock bar 5 provided at the rear of the pedestal 4, that is, provided on the fork 2 side of the order picking truck 1. The lock bar 5 is supported by the pedestal 4 and is rotatable upward and downward. Usually, the lock bar 5 is set parallel with the fork 2. After the lock bar 5 is inserted into a hole of the pallet 6 together with the fork 2, the lock bar 5 is rotated downward by operation conducted by an operator. In this way, the lock bar 5 pushes a lower deck board of the pallet 6 from above, so that the pallet 6 is locked. In order to release the lock of the lock bar 5, the operator conducts operation reverse to that conducted in the case of locking. By the reverse operation, the lock bar 5 is rotated upward and returned to the initial horizontal posture, so that the lock is released. The operator manually conducts the locking and unlocking operation by controlling a lever and a pedal arranged in the operator""s stand 3.
When the pallet 6 is oscillated on the fork 2 while the operator conducts reloading at a high place, there is a possibility that the load falls. Thus, the pallet should be locked. The lock is released when the fork is drawn out from the pallet, so that the pallet is placed on a shelf or ground.
As above described, the locking operation is very important. Accordingly, the operator positively executes the locking operation. However, the unlocking operation is not necessarily conducted at an appropriate timing. If unlocking operation is incompletely conducted when the fork is drawn out from the pallet which is set on a shelf, the fork or lock device is brought into contact with the pallet so that the pallet is drawn out together with the fork and falls from the shelf. If the lock is released before the pallet is surely placed on the shelf, the pallet becomes unbalanced and the pallet is oscillated on the fork depending upon a state of the load placed on the pallet, and there is a possibility that the load collapses.
Also, in case where the pallet 6 is locked according to the operator""s will, there is a possibility that the operator forgets to conduct the locking operation. In this case, the pallet 6 becomes unstable and the load may collapse.
The present invention has been accomplished to solve the above problems. An object of the present invention is to provide a forklift capable of positively releasing the lock of a pallet at an appropriate timing.
Another object of the present invention is to provide a forklift capable of positively locking the pallet at an appropriate timing.
According to a first aspect of the present invention, there is provided a forklift comprising: a fork to be inserted into a pallet; a hoisting device for hoisting the fork; and a pallet lock device for locking the pallet, the pallet lock device having a lock bar which is pushable a lower deck board of the pallet to lock the pallet, wherein the pallet lock device releases the lock of the pallet when an intensity of the force given to the lock bar from the lower deck board exceeds a predetermined value.
According to a second aspect of the present invention, the pallet lock device releases the lock of the pallet when the lock bar is displaced upward by the force given from the lower deck board.
According to a third aspect of the present invention, the pallet lock device comprises: a lock bar driver for moving the lock bar upward and downward; and a detector for detecting an upward displacement of the lock bar caused by the force given from the lower deck board, wherein the lock bar driver releases the lock of the pallet when the detector detects the upward displacement of the lock bar.
According to a fourth aspect of the present invention, the pallet lock device releases the lock of the pallet when the fork is operated to a state in which the fork is drawable out from the pallet.
According to the first to fourth aspects of the invention, the lock bar pushing the lower deck board of the pallet is given an upward force from the lower deck board when the fork is lowered and the pallet is placed on a shelf or ground. When an intensity of this upward force given from the lower deck board to the lock bar becomes higher than a predetermined value, it is judged that the pallet is placed, and the lock is automatically released. Therefore, it is unnecessary for an operator to manually conduct an unlocking operation. The lock is appropriately released, and the above problems are not caused. Since the unlocking operation is conducted after the pallet is placed on a shelf etc., the load on the pallet does not become unbalanced and does not collapse. The predetermined value must be set at a value higher than an intensity of the force given from the lower deck board to the lock bar when the forklift runs and the fork is oscillated upward and downward. If the predetermined value is set at an excessively low value, the lock is released each time the forklift runs and the fork is oscillated. Accordingly, the predetermined value must be set based on a value of the upward force given from the lower deck board to the lock bar when the forklift is running, which can be calculated, actually measured or estimated. And the predetermined value must be set at a value higher than the value of the upward force. The detector for detecting the force given from the lower deck board to the lock bar may be a sensor capable of detecting stress acting upward on the lock bar. Alternatively, the detector may be a sensor or switch for detecting an upward displacement of the lock bar which is displacably supported so that it can be displaced upward according to the force given from the lower deck board. Alternatively, the detector may be provided separately from the lock bar for detecting the force. The displacement of the lock bar may be electrically detected. Alternatively, the displacement of the lock bar may be detected by a mechanical means; which is mechanically linked with the displacement. The lock bar may be urged by a spring which pushes the lock bar downward when locking the pallet and pushes the lock bar upward when unlocking the pallet, so that lock bar is rotated.
According to a fifth aspect of the present invention, the lock bar is supported on the pallet lock device via an elastic member for elastically pushing the pallet.
According to the fifth aspect, the pallet is elastically pushed by the elastic member. Therefore, the lock bar can be easily displaced upward by a force given from the lower deck board. Further, dimensional error of the pallet hole in the vertical direction can be is absorbed by the elastic member.
According to a sixth aspect of the present invention, there is provided a forklift comprising: a fork to be inserted into a pallet; a hoisting device for hoisting the fork; a pallet lock device for locking the pallet; a pallet detector for detecting an insertion of the fork into the pallet; and an upward movement detector for detecting an upward movement of the fork, wherein the pallet lock device locks the pallet after the pallet detector detects the insertion of the fork into the pallet and the upward movement detector detects the upward movement of the fork of a predetermined distance.
According to the sixth aspect, after the pallet detector detects the insertion of the fork into the pallet and the upward movement detector detects an upward movement of the fork, the moving distance of which is not less than a predetermined value, the pallet lock device is driven and the pallet is locked. Therefore, the locking operation is automatically conducted irrespective of the operator""s will. Accordingly, there is no possibility that the operator forgets to lock the pallet, that is, there is no possibility of the occurrence of the above problems which are caused when the operator forgets to lock the pallet. Since the pallet locking operation is conducted after the pallet detector detects the insertion of the fork into the pallet, there is no possibility that the locking operation is conducted while the fork is not inserted into the pallet. There is no possibility of making a mistake of locking operation, thereby failure of the pallet lock device is prevented. Further, the locking operation of the pallet is conducted when an upward movement of the fork, the moving distance of which is not less than a predetermined value, is detected. Therefore, the locking operation can be positively conducted irrespective of the height of a place to which the pallet is conveyed. The pallet is not locked when the fork reaches a predetermined height from the ground but the pallet is locked when the fork is lifted by a distance not less than a predetermined value from the height where the pallet detector detects the insertion of the pallet. Say the predetermined value is set at 20 cm and the pallet is placed at a position of 100 cm height from the ground, the locking operation is automatically conducted when the pallet is lifted by the fork to a position of 120 cm height from the ground. In the same manner, in case where the pallet is placed at a position of 150 cm height from the ground, the locking operation is automatically conducted when the pallet is lifted by the fork to a position of 170 cm height from the ground. Accordingly, even in case where a plurality of pallets are piled, each pallet can be positively locked irrespective of the height.
According to a seventh aspect of the present invention, the upward movement detector detects the upward movement of the fork of the predetermined distance based on an operating time of the hoisting device.
According to the seventh aspect, in case where the lifting speed of the fork by the hoisting device is constant, it is possible to detect that the fork has reached a position, the height of which is not less than a predetermined value, by the product of the lifting speed and the operating time of the hoisting device. This enables a simple and inexpensive structure. In case where the lifting speed of the fork is not constant, it is possible to add a sensor for detecting the lifting speed and detect that the fork has reached a position, the height of which is not less than a predetermined value, by the product of the output of the sensor and the operating time of the hoisting device. In case where the hoisting device is operated during the continuous switch-on operation conducted by the operator, the above operating time is the same as the switch-on time. This structure can be easily implemented by a well known electric means.
According to an eighth aspect of the present invention, the hoisting device comprises a motor which is a drive source for hoisting the fork, wherein the upward movement detector detects the upward movement of the fork of the predetermined distance based on number of revolutions of the motor.
According to the eighth aspect, the lifting distance of the fork is substantially proportional to the number of revolutions of the motor. When the number of revolutions is detected and counted by an encoder and this counted value reaches a predetermined value, it is judged that the fork has reached a position, the height of which is not less than a predetermined value. This enables a simple and inexpensive structure.
According to a ninth aspect of the present invention, the pallet lock device comprises: a lock bar which is pushable a lower deck board of the pallet; and a lock bar driver for moving the lock bar upward and downward.
According to the ninth aspect, the pallet is locked when the lower deck board of the pallet is pushed from above by the lock bar. Therefore, the pallet can be positively locked, and further a load can be placed on the front face of an upper deck board on the pallet. Since the lock bar is driven upward and downward by the lock bar driver, the lock bar can be automatically driven.
According to a tenth aspect of the present invention, the pallet lock device releases the lock of the pallet based on an upward force given from the lower deck board to the lock bar.
According to the tenth aspect, the lock of the pallet is automatically released when the pallet on the fork is placed on the ground. Therefore, the pallet can be easily released from the fork.
According to an eleventh aspect of the present invention, there is provided a forklift comprising: a fork to be inserted into a pallet; a hoisting device for hoisting the fork; a pallet lock device for locking the pallet; and a pallet detector for detecting an insertion of the fork into the pallet, wherein the pallet lock device locks the pallet when the pallet detector detects that the pallet reaches to a predetermined position close to a base end portion of the fork.
According to a twelfth aspect of the present invention, the pallet lock device comprises: a lock bar which is pushable a lower deck board of the pallet, the lock bar having a tapered portion; and a lock bar driver for moving the lock bar upward and downward, wherein the tapered portion comes into contact with the pallet as the fork is inserted into the pallet and thereby the lock bar is tilted, wherein the pallet detector detects that the pallet reaches a predetermined position based on a tilting movement of the lock bar.
According to the eleventh and twelfth aspects, when the fork is inserted into the pallet, the pallet is automatically locked by the pallet lock device. Accordingly, there is no possibility of the occurrence of problems caused when the operator forgets to conduct pallet locking operation. Since the lock of the pallet is conducted when the pallet reaches to a predetermined position close to the base end portion of the fork, there is no possibility that the pallet is locked while the fork is being insufficiently inserted. Consequently, the fork is inserted into a sufficiently deep portion of the pallet and the pallet is locked by the pallet lock device. Therefore, sliding and oscillation of the pallet can be positively suppressed.
According to a thirteenth aspect of the present invention, there is provided a forklift comprising: a fork to be inserted into a pallet; a hoisting device for hoisting the fork; a pallet lock device for locking the pallet; and a pallet detector for detecting an insertion of the fork into the pallet, wherein the pallet lock device locks the pallet when the fork is hoisted by the hoisting device in state where the pallet detector detects the insertion of the fork into the pallet.
According to the thirteenth aspect, the pallet is automatically locked when the hoisting of the pallet is started. Accordingly, there is no possibility of the occurrence of problems caused when an operator forgets to lock the pallet. Further, it is possible to positively prevent the collapse of the load on the pallet and prevent the operator from falling from the pallet.
According to a fourteenth aspect of the present invention, there is provided a forklift comprising: a fork to be inserted into a pallet; a hoisting device for hoisting the fork; a pallet lock device for locking the pallet; and a fork position detector, wherein the pallet lock device locks the pallet when the fork position detector detects that the fork inserted into the pallet is located at the position close to the lower face of the upper deck board.
According to the fourteenth aspect, after the fork has been inserted into the pallet, when the fork is lifted to a position close to the lower face of the upper deck board of the pallet, the pallet is automatically locked by the pallet lock device. Accordingly, there is no possibility of the occurrence of problems caused when the operator forgets to lock the pallet. Since the pallet is locked when the fork is located at a position close to the lower face of the upper deck board of the pallet, oscillation of the pallet caused by the locking operation is reduced by the contact of the upper deck board with the fork. Accordingly, oscillation of the pallet can be positively prevented from the beginning to the end of the locking operation.
According to a fifteenth aspect of the present invention, there is provided a forklift further comprising a pallet detector for detecting an insertion of the fork into the pallet, wherein the pallet lock device locks the pallet when the pallet detector detects the insertion of the fork into the pallet and the fork position detector detects that the fork inserted into the pallet is located at a position close to a lower face of an upper deck board of the pallet.
According to the fifteenth aspect, there is no possibility that the pallet lock device is erroneously operated. Only when the fork is correctly inserted into the pallet, the pallet can be locked.
According to a sixteenth aspect, there is provided a forklift comprising: a fork to be inserted into a pallet; a hoisting device for hoisting the fork; and a pallet lock device for locking the pallet, wherein the pallet lock device comprises: a lock bar which is movable to a first position protruding from an upper face of the fork, a second position located lower than the first position, and a third position located lower than the second position and coming into contact with a lower deck board of the pallet; a detector for detecting a displacement of the lock bar from the first position to the second position; and a lock bar driver for displacing the lock bar to the third position when the detector detects the upward displacement of the lock bar.
According to the sixteenth aspect, when the fork is inserted into the pallet, the lock bar is located at the first position where the lock bar protrudes from an upper face of the fork. When the lock bar comes into contact with the pallet, it is pushed downward and displaced to the second position. Insertion of the pallet is detected by the detector as the lock bar displaces from the first position to the second position, and then, the lock bar driver is driven. The lock bar driver displaces the lock bar from the second position to the third position which is lower than the second position, so that the lock bar comes into contact with the lower deck board of the pallet. In this way, the pallet is locked. In other words, insertion of the fork into the pallet is automatically detected, and the pallet is automatically locked according to the result of detection. Therefore, problems caused when an operator forgets to lock can be positively solved. One lock bar is used for fulfilling two purposes, one is to detect insertion of the fork into the pallet and the other is to push the pallet. This enables a simplified structure.
According to a seventeenth aspect of the present invention, the fork lift is an order picking truck having an operator""s stand which is hoisted together with the fork, wherein the pallet lock device is disposed on the operator""s stand.